Support bed assemblies consisting of only impact bars, support bed assemblies consisting of impact bars and center impact rollers, and support bed assemblies consisting of slider bars and conventional, center non-impact rollers are known. Generally, support bed assemblies with impact bars are used in the impact or loading zone of conveyor belt systems where material to be conveyed is deposited on the conveyor belt, whereas support bed assemblies with the slider bars and center rollers are best adapted for use downstream of the impact zone for supporting the conveyor belt as it travels downstream with the material to be conveyed already deposited thereon.
Conventional slider bars have an upper plastic layer that is bonded to a metal base for use in support bed assemblies which, as mentioned, are generally outside of the impact zone where belts are loaded with material to be conveyed. Typically the plastic is an ultra high molecular weight polyethylene (UHMW) material that is bonded to a base of aluminum material. Because the polyethylene layer has low friction characteristics for supporting the belt to slide thereover, it is also difficult to bond directly to the aluminum base. In this regard, the UHMW layer tends to undesirably delaminate even under relatively low loading conditions.
Another problem with standard slider bars as described above is that the bonding of the UHMW layer to the aluminum base is a relatively expensive undertaking. For bonding the UHMW layer to the aluminum base, a bonding layer of adhesive foam is used which needs to be carefully laid down on the base, cut to length and set in place between the UHMW layer and the base. As is apparent, such a process is manual labor intensive and thus very costly.
Another known slider bar is thicker than the conventional lower profile slider bars and utilizes a hard urethane material molded to a lower metallic insert. The harder urethane material in these thicker slider bars is not of a resilience that will sufficiently absorb impact forces in the impact zone. Because of the high cost of the urethane material and its thickness, these thicker slider bars are also very expensive.
U.S. Pat. Nos. 5,038,924 and 5,103,967 to Stoll both disclose impact saddles that utilize multiple polymeric segments slid directly onto a support frame in a transverse direction relative to the belt travel direction. For this purpose, the segments are each provided with a pair of T-shaped slots that extend transversely across the width of the segments. The segments are each received in sequence on a corresponding pair of T-shaped support members of the support frame that extend transversely across and below the belt. To achieve impact absorption, rubber pads extend continuously along the upper surface of the support members so that they are received in the slots of each of the segments received thereon.
Thus, when mounted to the support frame, the length of the segments will extend orthogonal to the length of the T-shaped support members, and the polymeric material of the segments will extend upstream beyond the T-shaped support members. As the belt travels on these segments, forces urging the segments downstream will only be resisted by the support members creating a location for potential failure and requiring extra polymeric material upstream of the support members to minimize instances of such failure. In addition, Stoll discloses that the segments can be replaced by driving new segments onto the support frame from one side while the older segments come off the other side. However, this does not allow for efficient replacement of segments that may be more worn than others such as those located at the central area of the support frame where impact forces tend to be more heavily concentrated.
In the support bed assemblies best adapted for use in the impact zone, impact bars are utilized which are operable to absorb the impact forces generated by the heavy loads deposited onto the conveyor belt as it travels through the impact zone. For this purpose, in addition to including an upper plastic layer on which the belt is supported for sliding thereover, the impact bars include a body of elastomeric material bonded to the upper plastic layer. Thus, typical impact bars are thicker than low profile slider bars and even more expensive. Such support or impact bed assemblies and the construction of the impact bars therefor are described in Applicant's assignee's U.S. Pat. No. 7,815,040, which is incorporated as if reproduced in its entirety herein. The manufacture of the impact bars is relatively expensive since the elastomeric material itself can be relatively costly, and it is molded with a lower aluminum insert on which a bonding layer may be applied. An upper UHMW layer is utilized as in slider bars, and this layer may need to have its underside roughened and then have adhesive applied thereto for bonding the UHMW polyethylene layer to the upper surface of the elastomeric body. Thus, material costs, manual labor, and the manufacturing process make impact bars relatively expensive to produce.